All U.S. patents and patent applications cited below are herein entirely incorporated by reference.
Gels are generally formed when attractions between molecules (such as via hydrogen bonding, Van der Waals forces, ionic attractions, pi-pi interactions, etc.) facilitate the formation of an extensive three-dimensional strand network that traps and/or encapsulates (i.e., immobilizes) a solvent component between such strands (such as via hydrogen bonding). Gelling agents have been utilized in various applications for many years, particularly in terms of immobilizing certain solvents, mostly polar in nature, for improvements in storage and delivery thereof. Most importantly, and particularly for consumer purposes (personal care products, cosmetics, antiperspirants, etc.), gelling agents have been prominent in permitting utilization of difficult-to-handle and/or difficult to apply beneficial solvents and active ingredients within such consumer product formulations.
Generally, the presence of gelling agents provides formulation structure which, in turn, permits a more uniform and even application of desirable additives to target surfaces (skin, for example). Without such gelled systems, the solvents and/or actives present within such formulations would most likely precipitate out of solution or bloom to the surface, thereby creating a delivery problem with either too little or too great an amount applied to the target area. In particular, certain organic solvents may provide excellent skin treatment effects, yet, due to high volatility, such materials are difficult to store and difficult to actually apply to target surfaces without losing the efficacy thereof. Solid actives (for example aluminum salts in antiperspirants) are likewise difficult to keep in a stable uniform dispersion that can be applied evenly to target surfaces (axilla of humans, for instance).
As a result, it was realized in the past that delivery and storage systems for such highly volatile solvents and solid active ingredients were required and gels and/or solids were developed in response. Over the years, improvements in certain gelling materials has led to a number of results, some of great value, and some of limited usefulness. For instance, for antiperspirant sticks, certain expensive amide-based gelling agents were produced for low residue transfer and gelling of very specific silicone-based systems, and in particular, polar formulations. Such polar formulations create certain undesirable effects, such as high dissolution temperatures, solvent incompatibility, cracking, a lack of a clear gel thereof, a “wet” feeling upon application, and a reduction in certain degrees of efficacy of the active ingredients due to the loss of certain amounts of such actives dissolved within such polar components.
The ability to control and gel non-polar solvents (such as of a certain maximum dielectric constant, for instance) is believed to provide a manner of overcoming these limitations of amide/hydroxystearic acid-based gelling systems. Although such an amide/hydroxystearic acid gel has proven effective for personal care consumer applications to a certain extent, unfortunately such systems exhibit low versatility (in terms of solely gelling polar co-solvents, for example) and high costs, thereby providing a gelling agent of limited availability and diminished demand.
Another type of gelling agents used to make low residue antiperspirant sticks is dibenzylidene alditol (DBS) based compounds. Although these gelling agents can provide hard and stable polar solvent gels (like propylene glycol, isostearyl alcohol, etc.), they generally cannot efficiently gel non-polar solvents. Furthermore, the DBS gelling agents are not acid stable, and they have limited use in antiperspirant formulations because the antiperspirant actives are acidic in nature.
Furthermore, particularly within consumer applications, many gelling agents are limited in their versatility due to incompatibility with and/or instability in the presence of certain necessary additives, including, without limitation, emollients, waxes, fillers, antimicrobial agents, fragrances and other additives. Waxes in particular have proven troublesome, within antiperspirant stick formulations due to the ability of such components to crystallize therein. Once in crystallized form, such waxes have a tendency to migrate to the surface of the antiperspirant gel and, when the gelled formulation is applied to a target surface, such crystallized waxes will invariably leave a white residue thereon. Such aesthetically displeasing results have been combated against for many years without much improvement except for the removal of certain amounts of needed wax components, which are generally added to impart firmness, structure, and other physical properties to the target gel.
Thus, there is a distinct need to provide a cost-effective gelling agent that reduces and/or controls the level of crystallinity in the waxes therein in order to create a stable, clear gel and to prevent residue generation on treated surfaces. Unfortunately, except for the aforementioned expensive amide-based types, such gelling agents have not been provided within the pertinent consumer markets. Additionally, most gelling agents are highly susceptible to oxidation and discoloration when stored, particularly those comprising highly oxidative actives. A gelling agent exhibiting stability to oxidation, pH stability (2-10), and thermal stability (12 weeks at 45° C.), in addition to other properties, is thus desirable for aesthetic and practical purposes.
Additionally, many gelling agents fail to provide sufficient levels of water/film interface durability for utilization as vehicles for skin or other surface application formulations. The ability for such formulations to be substantive upon water contact can be an absolute necessity for proper long-term skin contact applications (such as for antiperspirants, cosmetics, sunscreens, and the like) and many current gelling agents fail to provide such a characteristic. Thus, in addition to the properties noted above, there is a desire for a film fixing water-repellent, or at least a water-resistant, gelling agent for such end uses. To date, such a result has not been forthcoming, particularly in combination with the other desirable properties noted above.
Bisurea and polyurea compounds are well known as organic thickeners and have been used in the field of lubricants. Recently, bisurea gelling agents have been used to gel high boiling point non-polar solvents, and the microstructures of the three dimensional networks thus formed have been studied. However, these bisurea gelling agents have high melting temperature and dissolution temperature in the solvents, or the formed gels are not stable in ambient conditions for long periods of time (i.e., shelf life of weeks and months). Thus, new gelling agents with lower dissolution temperature and excellent gel clarity and stability are needed.